The present invention is directed to network communications.
A communications network such as network 100 of FIG. 1 may include a plurality of stations or nodes (nodes A–F) coupled by transmission media (e.g., cable wire or optical fiber) providing a path for the transmission of data (e.g., E-mail, video, multimedia, or voice) between two or more nodes (e.g. transmission media 140 between nodes A and B, and transmission media 141 between nodes B and C). The data can be transferred in accordance with a network protocol (e.g., Internet Protocol (IP), asynchronous transfer mode (ATM), or synchronous optical network/synchronous digital hierarchy (SONET/SDH)) over optical transmission media. The network 100 may include one or more central nodes and one or more branch nodes connected by an inner ring 126 and an outer ring 146. In this type of network configuration (a dual-ring topology), data can be transmitted from a source node to a destination node (often through intermediary nodes) by transmitting data along one of the two rings (e.g., inner ring 126 and outer ring 146), where the rings have traffic flowing in opposing directions (clockwise direction 110 or counterclockwise direction 111). Control information can be routed in a direction opposite the control information's respective data. As data enters each successive node, local data is split off and transit data passes through the node along the ring. In addition, local data may be added at each node (i.e., transmit data), integrated with the transit data and forwarded on a respective ring to a next node in the network.
In a conventional network using a dual-ring topology, the network can become congested for a variety of reasons. Nodes may oversubscribe and add or forward more data than is expected. Congestion on one ring can in turn cause congestion on the other ring. Congestion management on a conventional network includes the use of logic to monitor and control congestion issues. In a conventional dual ring topology network, when a node is forwarding an excessive amount of transit traffic, the node may communicate its derived usage information to an immediately upstream node via the opposite ring. The upstream node may then adjust its transmission rate (e.g., stop adding data at the upstream node from the upstream node's host to the congested ring). However, in the conventional systems proposed, the usage information provided by a downstream node is limited. The previously proposed systems provide no means for monitoring congestion at other nodes in the network other than a single downstream node.
Data is received in a node (e.g., node B) along a transmission media (e.g., transmission media 140 of outer ring 146 (FIG. 1)). The data received is generally in packet format, where each packet has a header, indicating source and destination information. Data packets are routed using the destination information in the packet header to determine if the packet is destined for the local host (local traffic) or destined for a given ring (transit traffic).
Each node on the ring includes two full duplex ports. One is connected to the inner ring 126 and one is connected to the outer ring 146. A Spatial Reuse Protocol Forwarding (SRPF) block in the node arbitrates between the transit traffic and the host data received (transmit traffic), multiplexing the transit traffic and host data using SRP fairness logic, such as the fairness logic described in “The Cisco SRP MAC Layer Protocol”, by Tsiang and Suwala, RFC 2892 (August 2000). The SRP fairness logic is a transmission control logic, which attempts to ensure that nodes get equal usage. The SRP fairness logic determines if a node is sourcing or forwarding an excessive amount of traffic and either imposes rate controls and/or originates and propagates fairness information, requesting that an immediately upstream node adjust its transmission rate. The logic can also be used to prioritize packets and expedite the handling of priority packets.
The SRP fairness logic also includes logic for determining on which ring traffic from a given node is to be added. Typically, ring selection is determined based on a shortest path determination. When packets are received from a host, ring selection algorithms in the SRP fairness logic seek out the shortest path to a destination. By selecting the shortest path, system designers hope to make the best use of system resources. When making decisions regarding adding new packets to a given ring, conventional systems have not previously taken into consideration actual congestion on a given ring. When only path length is considered, added congestion can arise. For example, the traffic load might not be balanced between the two rings. As such, a packet added to a ring that is congested may take longer to traverse the shortest path than if the packet were placed on the other ring (i.e., transit time on the ring with less hop count may be longer than the transit time on the ring with less traffic).
For certain types of packets, other ring selection algorithms are used. For example, with multicast/broadcast traffic, there is no single destination. As such, the shortest path algorithm is not used. For multicast/broadcast traffic, ring selection for each packet can be made using media access control (MAC) addressing techniques. The traffic can be distributed to the rings by hashing the MAC address associated with the traffic. However, the traffic load will be bound to the MAC address distribution.